This research is concerned with the major cellular mechanisms for repair of radiation damage to DNA, and their interactions in order to provide the basis for understanding and controlling biological radiation effects. It is currently concerned with a distinct special DNA repair mechanism operating in newly germinated bacterial spores, with the mechanism of the photoenzymatic repair reaction and with photorepair in cultured mammalian cells. BIBLIOGRAPHIC REFERENCES: Nobuo Munakata and Claud S. Rupert. "Effects of DNA-Polymerase Defective and Recombination-Deficient Mutations on the Ultraviolet Sensitivity of Bacillus subtilis Spores," Mutation Research 27 157-159 (1975). Claud S. Rupert. "Enzymatic Photoreactivation: Overview." In Molecular Mechanisms for Repair of DNA, Part A (Edited by P. C. Hanawalt and R.B. Setlow) Plenum Publishing Corp. N.Y., 1975.